A base station fixedly allocates radio resources in frames to a mobile terminal that periodically generates traffic.
For example, the fixed allocation of radio resources is included in an IEEE 802.20 draft standard (IEEE P802.20/D2.1 Draft Standard for Local and Metropolitan Area Networks—Standard Air Interface for Mobile Broadband Wireless Access Systems Supporting Vehicular Mobility—Physical and Media Access Control Layer Specification).
The allocated radio resource is fixedly used for a mobile terminal without requiring a separate allocation message until the radio resource used is changed or the radio resource is deallocated. Therefore, a radio resource allocation message is not needed for every frame, which makes it possible to reduce overhead due to an allocation message.
Meanwhile, an error control algorithm is divided into an automatic repeat request (ARQ) scheme and a forward error correction scheme. That is, the automatic repeat request is performed in a data link protocol in an OSI model, and the forward error correction is performed in a physical layer.
A hybrid automatic repeat request (HARQ) protocol is a protocol related to the retransmission of packets having errors. The HARQ protocol combines symbols of a transmitted data packet and a retransmitted data packet and decodes the combined data, thereby reducing the number of times the data packet is retransmitted.
The HARQ protocol for controlling errors by combining the automatic repeat request and the forward error correction has also been used to control errors in packets in an orthogonal frequency division multiplexing access (OFDMA) communication system.
However, in the related art, when a fixedly allocated radio resource is used to transmit packets, the loss of packets and time delay occur due to errors in the detection of an HARQ response signal.
For example, it is assumed that a mobile station successfully receives a packet transmitted from a base station according to the HARQ protocol in a downlink, and transmits an acknowledgement (ACK) in response to the reception of the packet; however, the base station misidentifies the acknowledgement (ACK) as a negative acknowledgement (NAK) due to errors in the detection of the response signal.
In this case, first, when the base station uses a fixedly allocated radio resource to transmit a specific packet, the mobile station, which is a receiving station, receives the packet.
When the mobile station successfully receives the packet, the mobile station deletes reception symbol information of the packet from an HARQ receiving buffer and assumes that a new packet will be transmitted from the base station. Simultaneously, the mobile station transmits an acknowledgement (ACK) signal to the base station.
However, when errors occur in the detection of the response signal, the base station is likely to misidentify the acknowledgement (ACK) signal from the mobile station as a negative acknowledgement (NAK) signal. In this case, the base station retransmits the corresponding packet in response to the negative acknowledgement (NAK) signal.
However, since the mobile station determines that the packet transmitted from the base station is the next packet, the mobile station does not combine the symbol of the received packet with the symbols of the previous packets. Therefore, the packet is unnecessarily retransmitted to the mobile station, and the mobile station fails to receive the retransmitted packet. Since the mobile station fails to receive the packet, the mobile station transmits the negative acknowledgement (NAK) signal to the base station, and then the base station receiving the negative acknowledgement signal retransmits the packet to the mobile station.
Since the mobile station assumes that the next packet will be transmitted from the base station, the mobile station fails to receive the retransmitted packet. Therefore, the retransmission of the current packet is repeated several times.
For this reason, in the related art, the method of transmitting packets using a fixedly allocated radio resource according to the HARQ protocol has problems in that packets are redundantly retransmitted between the base station and the mobile station due to errors in the detection of a response signal, which results in the consumption of radio resources.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the related art that is already known in this country to a person of ordinary skill in the art.